Centrifugal separators (or centrifuges) generally employ a piece of equipment, generally driven by a motor, which puts an object in rotation around a fixed axis, applying force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and less density. For example, material densities for several substances are as follows:
Liquidsg per cm3Water at 4 C.1.0000Water at 20 C.0.998Gasoline0.70Mercury13.6Milk1.03
Solidsg per cm3Magnesium1.7Aluminum2.7Copper8.3-9.0Gold19.3Iron7.8Lead11.3Platinum21.4Uranium18.7Osmium22.5Ice at 0 C.0.92
Gases at STPg per cm3Air0.001293Carbon dioxide0.001977Carbon monoxide0.00125Hydrogen0.00009Helium0.000178Nitrogen0.001251
Organismsg per cm3Vegetative cells1.135Average spore1.305
There are many different kinds of centrifuges, including those for very specialized purposes. One type of separator includes a rotor rotatable around a rotational axis. Inside the rotor is formed an inlet chamber, a separation chamber connected to the inlet chamber, and an outlet chamber connected to the separation chamber, for liquid which has been cleaned of the substance. In the separation chamber a stack of several frusto-conical separation discs is arranged coaxially with the rotational axis. The separation discs are provided with distancing elements, which keep the discs at a distance from each other so that in pairs they form interspaces. The centrifugal separator also comprises means for conducting the liquid and the substance dispersed therein, during operation, from the inlet chamber to a central part of the disc interspaces in a way such that liquid flows radially outwardly in the interspaces.
The liquid mixture to be centrifugally treated is normally conducted into the interspaces via supply holes centrally located in the separation discs. The flow is directed essentially in the circumferential direction and the radially outwardly directed flow of liquid will take place in thin so-called Ekman-layers along the upper and underside of the separation discs. The radially outwardly directed flow of liquid is distributed in thin Ekman-layers. This means that the flow velocity in these layers becomes high and that the layer of substance, which during operation has been separated in an interspace and accumulates on a radially outwardly directed side of a separation disc. With conventional separators, there is a risk of having the substance entrained in the flow of the liquid. Centrifugal separators of this kind are commonly used in a marine context to clean water polluted by oil and do not substantially provide an acceptable solution.
The present invention provides a centrifugal separator which improves on the prior centrifuges by use of a novel separation mechanism.